Applicant's disclosure is generally directed towards the location of a mobile device within a communications network. It is well known to determine the location of a mobile device based on signals that are transmitted by the mobile device and received at a plurality of reference stations. When a location estimation technique is dependent on signal arrival time or signal transit time measurements, it is also well recognized that signal multipath is often highly deleterious to the accuracy of the location estimate. Multipath generally refers to the reflection of a signal or component of a signal off an object between a transmitter and a receiver.
In the context of a wireless network, a mobile device or mobile station may transmits an uplink signal to an access point or base station having a certain functional relationship (in terms of signal timing) with respect to downlink signals transmitted by a serving access point or base station. This functional relationship may permit an extraneous system to observe the transmissions between mobile devices and the access point, and by doing so, determine the time of transmission for a given signal from the mobile device.
Knowing or determining the time of transmission of a signal from a mobile device, and the time at which this same signal is received at a set of other observing stations (e.g., Wireless Location Sensors or WLSs), it is possible to obtain ranges representing the distance of the mobile device to each WLS. There is a need in the art, however, for a system and method to determine the location of a mobile device and to combat multipath effects.
In view of these needs, one embodiment of the present subject matter provides a method of estimating the location of a mobile device. The method may include determining the time of transmission of a first signal from a base station and receiving the first signal at the mobile device. A second signal may be transmitted from the mobile device, the second signal being a function of the first signal advanced by a timing parameter and a time of receipt of the second signal at a first reference station determined. A first range of the mobile device from the first reference station may then be determined as a function of the determined time of transmission of the first signal and the determined time of receipt of the second signal. A plurality of grid points may be provided in a geographic region, the plurality of grid points containing the first reference station, and a first relationship may be determined between the determined first range and a first range metric for each of the plurality of grid points. A second relationship may also be determined for each of the plurality of grid points whereby the first and second relationships may be compared. From this comparison a location of the mobile device may be determined.
Another embodiment of the present subject matter provides a method for estimating the location of a mobile device. The method may comprise the step of determining a range of a mobile device to a reference station as a function of the time of transmission of a first signal transmitted from a base station and as a function of the time of receipt of a second signal transmitted from the mobile device to the reference station, the second signal being a function of the first signal advanced by a timing parameter. The method may further include providing a plurality of grid points in a geographic region, the plurality of grid points containing the reference station. A relationship may be determined for each of the plurality of grid points as a function of the determined range and a range metric and then the determined relationship compared with data corresponding to each of the plural grid points. A location of the mobile device may then be determined as a function of the comparison.
A further embodiment of the present subject matter may provide a method for estimating the location of a mobile device in a geographic region including the step of determining a range of a mobile device to a reference station as a function of the time of transmission of a first signal transmitted from a base station and received by the mobile device and as a function of a second signal transmitted from the mobile device to a reference station, the second signal being a function of the first signal advanced by a timing parameter. The method may further include defining the geographic region by a plurality of grid points and determining a relationship for each of the plurality of grid points as a function of the determined range and a range metric. The determined relationship may then be compared with data corresponding to each of the plurality of grid points to determine a location of the mobile device.
An additional embodiment of the present subject matter provides a system for estimating the location of a mobile device. The system may include circuitry for determining a range of a mobile device to a reference station as a function of the time of transmission of a first signal transmitted from a base station and as a function of the time of receipt of a second signal transmitted from the mobile device to the reference station, the second signal being a function of the first signal advanced by a timing parameter. The system may further include a processor for determining a plurality of grid points in a geographic region, the plurality of grid points containing the geographic location of the reference station and may include circuitry for determining a relationship for each of the plurality of grid points as a function of the determined range and a range metric. Further, the system may provide circuitry for comparing the determined relationship with data corresponding to each of the plural grid points and may provide circuitry for determining a location of the mobile device as a function of the comparison.
These and other embodiments of the present subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal or the claims, the appended drawings, and the following detailed description.